Chamber liner for caseless ammunition firearms

ABSTRACT

A caseless ammunition firearm having a bore communicating with a barrel containing a caseless propellant and a projectile, the walls of the barrel containing a removable low thermal conductivity sleeve or liner fabricated of polytetrafluoroethylene.

United States Patent 1 Vassallo Oct. 30, 1973 CHAMBER LINER FOR CASELESS AMMUNITION FIREARMS [75] Inventor: Franklin A. Vassallo, Lancaster,

[73] Assignee: Cornell Aeronautical Laboratory,

Inc., Buffalo, NY.

[22] Filed: Apr. 26, 1971 [21] Appl. No.: 137,290

[52] [1.8. CI. 42/76 A, 89/16 [51} Int. Cl. F41c 21/12, F41f 17/06 [58] Field of Search 42/76 A; 89/16 [56] References Cited UNlTED STATES PATENTS 2,774,283 12/1956 Harvey 42/76 A 2,791,856 5/1957 Hartley 42/76 A Primary Examiner-Benjamin A. Borchelt Assistant ExaminerC. T. Jordan AttorneyAllen J. Jaffe [57] ABSTRACT A caseless ammunition firearm having a bore communicating with a barrel containing a caseless propellant and a projectile, the walls of the barrel containing a removable low thermal conductivity sleeve or liner fabricated of polytetrafluoroethylene.

4 Claims, 1 Drawing Figure PMENIEDBU 30 97 3.768.191

INVENTOR FRANKLIN A. VASSALLO ATTORNEY CHAMBER LINER FOR CASELESS AMMUNITION FIREARMS The invention hererin described was made under a contract with the Department of the Army.

BACKGROUND OF THE INVENTION The present invention relates to caseless ammunition firearms and, more particularly, to an improved chamber construction for caseless ammunition.

Presently used caseless ammunition generally introduces a much greater heat input to the chamber of the firearm in which the caseless ammunition is used. This is due to the absence of the case. In some situations the heat input is of such magnitude that continuous rapid fire of the firearms produces large temperatures in the chamber wall material. Because chamber temperatures cannot be allowed to exceed the cook-off or autoignition temperature of the caseless ammunition propellant, usually about 350F, operation of firearms utilizing caseless ammunition is severely limited by the imposed chamber heat load.

Techniques are known by which the ammunition itself is coated with an organic plastic. Such techniques, while effective in reducing net heat flow to the chamber, suffer from the problem of removal of excess plastic coatings which may remain in the chamber after the propellant has been burned. Also, since each round must be coated with a prescribed amount of plastic, manufacturing difficulties are increased.

SUMMARY OF THE INVENTION The foregoing difficulties of prior devices are overcome according to the teachings of the present invention.

The present invention provides a chamber liner fabricated of a plastic material which reduces chamber heating without excessive erosion or deterioration of the liner. Thus the chamber wall is protected and no material is left which has to be removed after the propellant has burned.

It has been found, contrary to normal expectations, that a chamber liner fabricated of polytetrafluoroethylene experiences little or no deterioration after firing a number of rounds. Although the reason for this unusual and unexpected resistance to deterioration while providing an effective barrier to heat transfer is not known, it is suspected that the normally low vaporization temperature of the polytetrafluoroethylene is increased considerably at the extreme ballistic pressures (about 50,000 psi) encountered during propellant combustion.

Basically, the present invention provides a caseless ammunition firearm having a bore communicating with a barrel, caseless propellant located in the barrel for propelling an adajcent projectile through the bore and a removable low thermal conductivity sleeve in the barrel fabricated of polytetrafluoroethylene.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of the present invention, reference should be had to the accompanying drawing wherein the only FIGURE is a fragmentary longitudinal sectional view of the caseless ammunition firearm according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing the caseless ammunition firearm is depicted schematically at 10 and comprises a barrel 12 having a central longitudinal bore 14 which communicates with an enlarged cylindrical chamber wall 16 via a substantially frusto-conical transition surface 18. A conventional bolt 20 is provided in slidable sealing contact with wall 16 and having a firing pin 22 passing through a central passage 24 thereof.

A projectile 26 is located in bore 14 and is adapted to be actuated by the ignition of a caseless propellant 28 between the firing pin and the projectile. Propellant 28 may be of a molded caseless construction as is well known.

A cylindrical sleeve or liner 30 fabricated of polytetrafluoroethylene is tightly or press fitted into chamber wall 16 in surrounding relation to the propellant 28 and projectile 26. i

In operation, when propellant 28 is ignited the explosive forces generated force the projectile through bore 14. The liner 30, being of a low thermal conductivity, functions to insulate the wall 16 from the high temperature generated by the burning propellant. The liner limits the temperature rise of the chamber wall 16. Although the behavior of polytetrafluoroethylene in the high temperature and pressure environment of the burning propellant is contrary to normal expectations, it has been found that such a liner has been effective to protect the barrel wall without any significant deterioration thereof. It is suspected that the normally low vaporization temperature of the polytetrafluoroethylene is increased considerably when operating at the extreme ballistic pressure encountered during propellant combustion, which is about 50,000 psi. It is likely that as the surface temperature of the polytetrafluoroethylene increases due to heating fromthe propellant gases, the accompanying chamber pressure remains considerably above the vapor pressure of the polytetrafluoroethylene preventing vapor loss. Thus, the chamber liner provides an effective barrier to heat flow to the chamber wall. The number of rounds that can be fired prior to achieving auto-ignition temperatures in the chamber wall is greatly increased.

As an example with a 0.05 inch thick liner in a chamber normally utilized for 7.62 mm caseless ammunition and atrelatively low firing rates the number of rounds permitted before cook-off would be about three times as many as would be permitted without the use of the liner.

Although a preferred embodiment has been disclosed and described, changes will occur to those skilled in the art. It is therefore intended that the invention is to be limited only by the scope of the appended claims.

I claim:

1. A caseless ammunition firearm comprising;

a. a bore,

b. a barrel communicating with said bore,

c. a caseless propellant in said barrel,

d. a projectile in said bore and e. a removable sleeve fitted into said barrel in surrounding relation to said caseless propellant and fabricated of a low thermal conductivity material.

2. The apparatus according to claim 1, wherein;

f. said low thermal conductivity material is polytetrafluoroethylene.

3. The apparatus according to claim 2, wherein; and

g. said sleeve is press fitted into said barrel. i. the internal diameter of said sleeve is equal to the 4. The apparatus according to claim 3, wherein; diameter of said bore.

h. said barrel has a larger diameter than said bore, 

1. A caseless ammunition firearm comprising; a. a bore, b. a barrel communicating with said bore, c. a caseless propellant in said barrel, d. a projectile in said bore and e. a removable sleeve fitted into said barrel in surrounding relation to said caseless propellant and fabricated of a low thermal conductivity material.
 2. The apparatus according to claim 1, wherein; f. said low thermal conductivity material is polytetrafluoroethylene.
 3. The apparatus according to claim 2, wherein; g. said sleeve is press fitted into said barrel.
 4. The apparatus according to claim 3, wherein; h. said barrel has a larger diameter than said bore, and i. the internal diameter of said sleeve is equal to the diameter of said bore. 